Probably something to do with the fact that the game was (allegedly) pulling in ~$50k/day at the top of the charts in iTunes with very little focus on monetization.
That was combined with an exceedingly simply UX anyone could understand.
And then the developer, to many people's shock, decided to pull the game. He said he didn't want the attention.
Like all popular games - especially the simple ones - there have indeed been a ton of clones pouring into the store.
Although a beginner could have some fun coding a clone.